Chiral Helicates Research Articles

Asymmetric Synthesis of Tetraphenylethylene Helicates and Their Full-Color CPL Emission with High glum and High Fluorescence Quantum Yield.

Tetraphenylethylene (TPE) helicates with single helical handedness not only owe high fluorescence quantum yield but also possess good helical chirality, showing an excellent circularly polarized luminescence active material. In this work, a new method for directly obtaining single-handed TPE helicates has been developed. By using chiral p-phenylenediamine derivatives as an intramolecular cyclization reagent of TPE, the single-handed propeller-like conformation and stable helical chirality of the TPE unit were obtained, avoiding complicated and expensive HPLC chiral column separation. The as-prepared chiral TPE helicates displayed strong emission with an almost quantitative fluorescence quantum yield (Φf) and strong circularly polarized luminescence (CPL). In addition, the chirality and CPL signals of the TPE helicates could be significantly magnified by the helical arrangement together with 4'-pentyl-4-biphenylcarbonitrile (5CB) liquid crystal molecules. Moreover, full-color CPL emissions with both a high absolute CPL dissymmetrical factor up to 0.43 and high Φf were afforded.

Remarkable 980 nm circularly polarized luminescence from dinuclear Yb(iii) helicates with aD4symmetry

Chiral BINOL-modified dinuclear helicates Yb2(R/S-BTHP)4show the excellent NIR-CPL at 980 nm with theglumreaching up to 0.81 andBCPLbeing up to 821 M−1cm−1.

Stereoselective Self-Assembly of DNA Binding Helicates Directed by the Viral β-Annulus Trimeric Peptide Motif.

Combining coordination chemistry and peptide engineering offers extraordinary opportunities for developing novel molecular (supra)structures. Here, we demonstrate that the β-annulus motif is capable of directing the stereoselective assembly of designed peptides containing 2,2′-bipyridine ligands into parallel three-stranded chiral peptide helicates, and that these helicates selectively bind with high affinity to three-way DNA junctions.

Fine-Tuning of Chiral Microenvironments within Triple-Stranded Helicates for Enhanced Enantioselectivity.

Here we report the formation of an unexpected and unique family of chiral helicates. Crystal structures show that these triple-stranded ZnII2 L3 complexes are held together by subcomponent assembly of axially chiral diamine-functionalized 1,1'-biphenol ditopic with 2-formylpyridine and ZnII . Specifically, the molecular helicity of the complexes can be controlled by the absolute configurations of the bimetallic vertices, which has been shown to be homoconfiguration (ΔΔ) or mesomeric configuration (ΔΛ), depending critically on the bulky groups and length of the spacers. Fascinatingly, in this system we can engineer the space-restricted chiral microenvironments with varied polar and apolar moieties, which profoundly influence the binding affinities and chiral discrimination properties of the helicates, leading to highly enantio- and helix-sense-selective recognition for chiral amino alcohols (up to 9.35). This work reveals the transformation of single-molecule chirality to global supramolecular chirality within well-defined helicates and demonstrates that their chiral discrimination are highly dependent on the superior microenvironments.

Fine‐Tuning of Chiral Microenvironments within Triple‐Stranded Helicates for Enhanced Enantioselectivity

AbstractHere we report the formation of an unexpected and unique family of chiral helicates. Crystal structures show that these triple‐stranded ZnII2L3 complexes are held together by subcomponent assembly of axially chiral diamine‐functionalized 1,1′‐biphenol ditopic with 2‐formylpyridine and ZnII. Specifically, the molecular helicity of the complexes can be controlled by the absolute configurations of the bimetallic vertices, which has been shown to be homoconfiguration (ΔΔ) or mesomeric configuration (ΔΛ), depending critically on the bulky groups and length of the spacers. Fascinatingly, in this system we can engineer the space‐restricted chiral microenvironments with varied polar and apolar moieties, which profoundly influence the binding affinities and chiral discrimination properties of the helicates, leading to highly enantio‐ and helix‐sense‐selective recognition for chiral amino alcohols (up to 9.35). This work reveals the transformation of single‐molecule chirality to global supramolecular chirality within well‐defined helicates and demonstrates that their chiral discrimination are highly dependent on the superior microenvironments.

Dynamic Stereoselection of Peptide Helicates and Their Selective Labeling of DNA Replication Foci in Cells**

AbstractAlthough largely overlooked in peptide engineering, coordination chemistry offers a new set of interactions that opens unexplored design opportunities for developing complex molecular structures. In this context, we report new artificial peptide ligands that fold into chiral helicates in the presence of labile metal ions such as FeII and CoII. Heterochiral β‐turn‐promoting sequences encode the stereoselective folding of the peptide ligands and define the physicochemical properties of their corresponding metal complexes. Circular dichroism and NMR spectroscopy in combination with computational methods allowed us to identify and determine the structure of two isochiral ΛΛ‐helicates, folded as topological isomers. Finally, in addition to the in‐vitro characterization of their selective binding to DNA three‐way junctions, cell‐microscopy experiments demonstrated that a rhodamine‐labeled FeII helicate was internalized and selectively stains DNA replication factories in functional cells.

Dynamic Stereoselection of Peptide Helicates and Their Selective Labeling of DNA Replication Foci in Cells*.

Although largely overlooked in peptide engineering, coordination chemistry offers a new set of interactions that opens unexplored design opportunities for developing complex molecular structures. In this context, we report new artificial peptide ligands that fold into chiral helicates in the presence of labile metal ions such as FeII and CoII . Heterochiral β-turn-promoting sequences encode the stereoselective folding of the peptide ligands and define the physicochemical properties of their corresponding metal complexes. Circular dichroism and NMR spectroscopy in combination with computational methods allowed us to identify and determine the structure of two isochiral ΛΛ-helicates, folded as topological isomers. Finally, in addition to the in-vitro characterization of their selective binding to DNA three-way junctions, cell-microscopy experiments demonstrated that a rhodamine-labeled FeII helicate was internalized and selectively stains DNA replication factories in functional cells.

Chiral BINAPO Induced Circularly Polarized Luminescence in a Triple-Stranded Eu2L3(BINAPO)2 Helicate

Chiral lanthanide helicates with circularly polarized luminescence (CPL) properties have found potential application in bioanalyses and chirality sensing. However, the preparation of the enantiopure helicates through a coordination-directed self-assembly strategy is challenging due to the greatly labile coordination geometries of lanthanide ions. Herein, a pair of enantiopure triple-stranded EuIII helicates [(Eu2L3)(R/S-BINAPO)2] are assembled by three achiral C2-symmeric bis-β-diketones (4,4′-bis(4,4,4-trifluoro-1,3-dioxobutyl)(phenoxyl)-1,1′-biphenyl, L) helically twisting around two EuIII ions, and two chiral R/S-bis(diphenylphosphoryl)-1,1′-binaphthyl (R/S-BINAPO) as ancillary ligands. Electrospray ionization–mass spectrometry, NMR, and circular dichroism (CD) spectra confirm the formation of a pair of enantiopure chiral topological helicates (Eu2L3)(R-BINAPO)2 and (Eu2L3)(S-BINAPO)2. As expected, the helicates present strong CPL with the |glum| up to 0.09, and the higher luminescent quantum yields (QYs) of up to 51%.

The Promise of Self-Assembled 3D Supramolecular Coordination Complexes for Biomedical Applications.

In the supramolecular chemistry field, coordination-driven self-assembly has provided the basis for tremendous growth across many subdisciplines, spanning from fundamental investigations regarding the design and synthesis of new architectures to defining different practical applications. Within this framework, supramolecular coordination complexes (SCCs), defined as large chemical entities formed from smaller precursor building blocks of ionic metal nodes and organic multidentate ligands, resulting in intricate and well-defined supramolecular structures, hold great promise. Notably, interest in the construction of discrete 3D molecular architectures, such as those offered by SCCs, has experienced extraordinary progress because of their potential application as sensors, catalysts, probes, and containers and in basic host-guest chemistry. Despite numerous synthetic efforts and a number of inherent favorable properties, the field of 3D SCCs for biomedical applications is still in its infancy. This Viewpoint focuses on 3D SCCs, specifically metallacages and helicates, first briefly presenting the fundamentals in terms of the synthesis and characterization of their host-guest properties, followed by an overview of the possible biological applications with representative examples. Thus, emphasis will be given in particular to metallacages as drug delivery systems and to chiral helicates as DNA recognition domains. Overall, we will provide an update on the state-of-the-art literature and will define the challenges in this fascinating research area at the interface of different disciplines.

The Construction of Homochiral Lanthanide Quadruple-Stranded Helicates with Multiresponsive Sensing Properties toward Fluoride Anions.

A series of unique homochiral lanthanide tetranuclear quadruple-stranded helicates have been self-assembled controllably by using the intrinsic advantages of chiral bridging ligands, (S)-H2 L and (R)-H2 L, and lanthanide ions with high coordination numbers. The self-assembly process of these chiral helicates not only ensures the structural stability and quadruple-stranded feature of lanthanide cluster in the solid state and solution, but also achieves effective transfer and amplification of the chirality code from the ligand to a higher supramolecular level. Moreover, through using optical rotation, circular dichroism spectra analysis, and luminescence measurements, we demonstrate that these chiral lanthanide helicates could serve as sensitive and multi-responsive sensors to recognize and detect F- anions based on the change of chiral signal and NIR luminescence simultaneously, which represents a meaningful exploration for developing functional lanthanide-based polynuclear clusters.

Stereocontrolled self-assembly of luminescent lanthanide helicates and their enantiodifferentiation using Δ-TRISPHAT as the NMR resolving agent

Self-assembled supramolecular lanthanide constructs have great potential in luminescent bioprobes/sensors. Stereoselectivity on the lanthanide assemblies is needed to facilitate chiroptical probes and sensors. Herein we report the stereocontrolled synthesis of M2L3-type (M=metal ion, L=organic ligand) lanthanide triple-helicates using a chiral-induction strategy, where the periphery point-chirality [(R,R) or (S,S)] of the organic ligands was transferred into the metal centered chirality (ΔΔ or ΛΛ), thus leading to the formation of topological chiral (P or M) helicates. Moreover, commercially available Δ-TRISPHAT proved to be an effective NMR chiral resolving agent to differentiate between the two enantiomers of the helicate.

Programmed stereoselective assembly of DNA-binding helical metallopeptides.

A flexible and versatile synthetic approach for the construction of water-stable DNA-binding chiral peptide helicates based on the solid phase peptide synthesis (SPPS) methodology is reported.

Chiral Supramolecular Frameworks Based on Chiral Metallocycles: Crystal Structures and Photophysical Properties

AbstractFour purely chiral supramolecular frameworks were constructed from a new chiral terpyridyl ligand, (S)‐2{4‐[2,6‐bis(pyridin‐2‐yl)pyridin‐4‐yl]benzylamino}propanoic acid (H2ptpy). The resulting compounds 1–4, namely [Cd2(Hptpy)2(Ac)2]·3CH3OH·H2O (1) [Ni2(Hptpy)2(CH3OH)(H2O)](ClO4)2·CH3OH·H2O (2), [Ni2(Hptpy)2(H2O)2](SCN)2 (3), and [Cu2(Hptpy)2](dca)2·4H2O (4) (Ac = acetate and dca = dicyanamide) all consist of those chiral metallocyclic units. As expected, those chiral nanometallocycles not only induced a chiral array or helicates but also amplified chirality through hydrogen‐bonding interactions, and finally aggregated into complicated higher‐dimensional chiral supramolecular architectures with chiral voids for further use. The formation of the metallocyclic units is easily monitored by UV/Vis spectra. Spectrophotometric titrations were performed by titrating Na(Hptpy) with a soltution of Cd(Ac)2 in methanol, and the global stability constants of [Cd2(Hptpy)2]2+ (log β = 17.60) were calculated. In combination with the structural analyses and UV/Vis and ES mass spectra, it is tentatively deduced that metallocycle units in 1–4 are the thermodynamically favored species in solution. Both the chiral H2ptpy ligand and 1 in the solid state and in solution display purple emission. The bathochromic shift of 1 is mainly due to the bichelation and intrametallocyclic π–π interactions.

Coordination Polymers and Metal Organic Frameworks Derived from 1,2,4-Triazole Amino Acid Linkers

The perceptible appearance of biomolecules as prospective building blocks in the architecture of coordination polymers (CPs) and metal-organic frameworks (MOFs) are redolent of their inclusion in the synthon/tecton library of reticular chemistry. In this frame, for the first time a synthetic strategy has been established for amine derivatization in amino acids into 1,2,4-triazoles. A set of novel 1,2,4-triazole derivatized amino acids were introduced as superlative precursors in the design of 1D coordination polymers, 2D chiral helicates and 3D metal-organic frameworks. Applications associated with these compounds are diverse and include gas adsorption-porosity partitioning, soft sacrificial matrix for morphology and phase selective cadmium oxide synthesis, FeII spin crossover materials, zinc-b-lactamases inhibitors, logistics for generation of chiral/non-centrosymmetric networks; and thus led to a foundation of a new family of functional CPs and MOFs that are reviewed in this invited contribution.

Supramolecular double helical Cu(i) complexes for asymmetric cyclopropanation

Chiral double-stranded helicates, formed between Cu(I) ion and C(2)-symmetric oligopyridines, were used for catalytic asymmetric cyclopropanation of alkenes; low catalyst loadings (0.2 mol%), high TONs (up to 404) and short reaction times (30-60 min) were achieved with [Cu(2)L(2)]OTf(2)(L = chiral C(2)-symmetric terpyridine).

Heterometallic Compounds Assembled from Ferrocene-Containing Bisthiosemicarbazone Clips

Heteropolynuclear organometallic compounds have been constructed by using the ferrocene-based ligand H(2)L, [NH(2)SCNHN=C(CH(3))(C(5)H(4))](2)Fe. Reaction of the ligand H(2)L with the cobalt(II) salt gave a tetranuclear helicate Co(2)Fe(2) (1) with two ferrocene-based clips wrapped around the two cobalt atoms. The chiral helicates recognized the neighbors with same chirality through intermolecular hydrogen bonding between the thiosemicarbazone moieties to form a one-dimensional chiral channel. Reaction of the ligand H(2)L with the cadmium(II) salt afforded a tetranuclear dimeric compound Cd(2)Fe(2) (2), with two symmetric related parts bridged through two sulfur atoms. Reaction of the ligand H(2)L with the copper(I) salt, in the presence of triethylamine, resulted in a hexanuclear compound Cu(4)Fe(2) (3) with a crownlike Cu(4)S(4) octagon similar to that of S(8) sited inside and two ferrocene-containing ligands positioned outside. Electrochemical measurements were displayed to investigate the redox communications between the ferrocene moieties through metal centers.

Tapes of Cyclic Water Tetramers in the Double‐Helical Complex[Cd2(bpa)2Cl4]·6 H2O

AbstractThe new complex [Cd2(bpa)2Cl4]·6 H2O [bpa = N,N'‐bis(picolinamide)azine] has been synthesized in which each bpa ligand is twisted into a spiral‐like conformation and the two CdII ions are ligated by two bpa ligands to form a double‐stranded binuclear helicate. Unprecedented water chains featuring cyclic water tetramers composed of three independent water molecules are trapped by [Cd2(bpa)2Cl4] double helicates by hydrogen bonds. The binuclear chiral helicates are interlinked into homochiral layers by hydrogen bonds with the water tapes. The layers are alternately stacked in a heterochiral fashion to yield the final racemic structure. The complex shows an endotherm at 65.7 °C in the DSC due to loss of water molecules, giving an enthalpy value of 47 kJ mol–1 per water molecule. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Cholesterol-Armed Cyclens for Helical Metal Complexes Offering Chiral Self-Aggregation and Sensing of Amino Acid Anions in Aqueous Solutions

Cholesterol-armed cyclens worked as octadentate receptors for Na+, Ca2+, and Y3+ complexes in which four chiral cholesterol-functionalized sidearms were bundled and asymmetrically twisted above cyclen-metal complex platforms. Since the resulting helical metal complexes included chiral, hydrophobic cholesterol residues and charged, hydrophilic metal sites as well as asymmetric coordination geometries, they exhibited unique amphiphilic properties and provided chiral self-aggregates in aqueous solutions. Light scattering, fluorescence, and TEM characterizations demonstrated that Na+ complex with cholesterol-armed cyclen gave a particularly stable self-aggregate in aqueous solution and offered supramolecular environments effective for sensing and detection of amino acid anions. Various dansylamino acid derivatives (dansyl = 5-(dimethylamino)-1-naphthalenesulfonyl) were nicely accommodated in the helicate aggregates to give highly enhanced fluorescence signals, which could be detected by the naked eye at 10(-7) mol/L level. Their inclusion behaviors were analyzed by a Langmuir-type equation, indicating that enantiomer-selective inclusion occurred. MM/MD calculations and circular dichroism (CD) studies further suggested that cholesterol-armed cyclen helicates have chiral and hydrophobic cavities upon self-aggregation, in which the dansylamino acid anions were specifically accommodated. Since these helicates exhibited nonselective binding abilities in solvent extraction experiments of dansylamino acid anions, uncommon chiral recognition and sensing functions were generated by supramolecular alignments of the chiral metal helicates in the aqueous solutions.

Enantiomeric interpenetrating 3D nets with chiral silver helicates

A new enantiomeric interpenetrating 3D nets with chiral helical coordination silver(i) polymer was achieved via self-assembly using the new ligand modular approach, in which the special helical conformation of the ligand provided the opportunity to translate chirality from one metal center to others.

Copper(I) Ion Mediated Self-Assembly of Triple-Stranded Helicates from Oligo(2-ethynylpyridines): Synthesis, Structure, and Properties

Abstract The reaction of oligo(2-ethynylpyridines) (L1–L8) with copper(I) ions proceeded smoothly to afford tri-, tetra-, and pentanuclear triple-stranded helicates (CL1–CL8) in good yields. If a chiral ligand was used, the stereoselective self-assembly of chiral helicates with one particular chirality was achieved in the solid state. Racemization of copper(I) helicates was also observed in solution.